I might add:
Laurent le Magnifique(French original title) by Ivan Cloulas ( a Renaissance expert who also wrote a volume on Catherine de Medici)

I greatly enjoyed the work, not only for the biography itself, but also for the chapters dealing with the commercial success of Lorenzo's ancestors (you can really understand how their system worked) and with the various figures that formed his retinue.
I also appreciated the book for the artistic material(it contains most of Lorenzo's own poems as well as the history behind the most important Renaissance masterpieces created during his rule)